Preparation of metal bromides from a basic metal compound and bromine in the presence of a reducing agent has been known for a long time.
For example, U.S. Pat. No. 1,775,598 discloses the use of reducing agents which are converted into water and/or gases. These may be nitrogen-containing organic or inorganic compounds such as urea, cyanamide, ammonia, ammonium carbonate, ammonium bicarbonate, formamide, carbamates, and ammonium cyanide; or easily decomposable organic acids such as formic or oxalic acid; or ammonium or metal derivatives of these compounds (e.g. calcium nitride, metal formates, or oxalates). Substances which give similar reducing agents on mixing (e.g. hexamethylenetetramine) also are disclosed. British Patent No. 285,915 has a similar disclosure.
U.S. Pat. No. 1,843,355 discloses use of charcoal as a reductant. U.S. Pat. No. 1,863,375 and 2,007,758 both relate to the use of ammonia as the reducing agent. U.S. Pat. No. 1,916,457 pertains to the use of carbon as a reductant, principally in the formation of sodium bromate.
U.S. Pat. No. 2,269,773 also discloses the use of a variety of reducing agents and alternative reaction sequences. U.S. Pat. No. 4,083,942 discloses the use of formic acid as a reactant, and illustrates the process with the following equation: EQU Ca(OH).sub.2 +HCOOH+Br.sub.2 .fwdarw.CaBr.sub.2 +CO.sub.2 +2H.sub.2 O
In the process of that patent, bromine and the alkaline compound are alternatively and incrementally added to an aqueous mixture of formic acid and a less than equivalent amount of metal compound, while maintaining the pH below 7.0.
U.S. Pat. No. 3,462,241 relates to the reaction of lime and bromine in the absence of a reductant: EQU 2Br.sub.2 +2Ca(OH).sub.2 .fwdarw.Ca(OBr).sub.2 +2H.sub.2 O+CaBr.sub.2
The yield of calcium bromide by this method is about 9-12%.
More recently, it was disclosed in U.S. Pat. No. 4,248,850 that metal bromides could be prepared by contacting in an aqueous medium a basic metal compound and bromine in the presence of added formaldehyde as a reducing agent. While this method affords certain advantages over those prior art processes which use nitrogen-containing organic or inorganic compounds as reducing agents--namely the elimination of foaming problems due to the liberation of nitrogen gas formed during the reaction, the use of formaldehyde as a reductant often results in the presence of unreacted formaldehyde in the product mixture which is difficult to remove and thereby adds to the cost of producing the desired metal bromide products.
In U.S. Pat. No. 3,431,068, there is disclosed a method of preparing alkali metal halides by reacting an alkali metal hydroxide with an elemental halogen in a liquid, saturated aliphatic or alicyclic alcohol or ketone, or a saturated aliphatic aldehyde. According to this process, the formation of unwanted halate salt by-products associated with alkali metal halide production is diminished or eliminated.
It has now been discovered that metal bromides can be prepared in high yields by contacting a basic metal compound, in particular an alkaline earth metal compound, in an aqueous medium with bromine in the presence of a lower alkanol as a reducing agent whereby those problems inherent in using formaldehyde as a reductant, aforediscussed, are eliminated.